Abstract: New experimental data for the viscosity of molten sodium nitrate from its melting point up to 752 K, at atmospheric pressure, with an estimated uncertainty of 2.1%, were measured with an oscillating cup viscometer. A preliminary reference correlation and reference data are proposed, based on the best available data for the viscosity of molten sodium nitrate, for temperatures between 590 and 750 K, with an estimated absolute uncertainty of 0.066 mPa.s (k = 2).

Abstract: The transport properties of molten salts at high temperatures are crucial for the efficient design of industrial equipment and chemical processes involving these materials. However, large discrepancies among the data published by different authors and different laboratories still exist, mostly caused by the difficulties in accurate measurements. This situation with regard to thermal conductivity and viscosity is especially serious for plant design. The aim of this paper is to demonstrate the implications of the uncertainty of molten salt thermophysical properties, such as thermal conductivity and viscosity, on the design of heat exchangers and other equipment. Some of the recent applications of ionic liquids at high temperatures, both as heat-transfer and chemical-reaction media, will be presented in order to illustrate how the knowledge of thermophysical properties is important for proper and optimal technological design, using two examples (thermal storage in solar plants and molten salt oxidation of wastes) among the many possible. The results obtained support that the implementation of those applications needs a careful selection of experimental data; other-wise, equipment will be either under- or overdimensioned, with the consequent poor operation or increased capital costs.

Abstract: The object of this work was to evaluate the influence of the meniscus of liquid in the determination of viscosity by the oscillating-cup method. We measured the viscosity of water at 298.15 K with several heights of water inside the cup. Results obtained allow us to state that, if the cup is not almost completely filled, errors in the viscosity measurements can be larger than the uncertainty of the method. But, if the cup is filled up to 95% of the total height, the error in the viscosity determination can be smaller than 0.1%.

Abstract: Potassium nitrate (KNO3) has been suggested as a standard material for the viscosity of molten salts, under moderate to high temperatures. A recently developed oscillating-cup viscometer has been tested up to 760 K, by measuring the viscosity of molten KNO3 at atmospheric pressure. A detailed analysis of the uncertainty of the measurements, and the comparison with the data reported by other authors, demonstrated that the data obtained had an estimated uncertainty of 2.3%.